Quantum cryptography transmission method and system
Quantum cryptography by polarization ambiguity is generally used but it involves polarization-maintained fibers. This invention proposes an alternative: quantum cryptography by ambiguity in time. It comprises the conversion of K bits to be transmitted into a train of K pulses of particle flows of time width ΔT and whose frequency Tb, is predetermined knowing that each of the K pulses being shifted or not in time such that the kth pulse is shifted by a duration t0 respectively t1, with respect to the initial instant of the period depending on the value “0”, respectively “1” of the kth bit, where k is an integer such that 0≦k<K and the shifts t0 and t1 are such that 0≦t0,t1≦Tb−ΔT and 0<|t1−t0|<ΔT.
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The invention concerns the field of cryptography.
RELATED APPLICATIONSThe present Application is based on International Application No. PCT/FR01/03500 filed on Nov. 9, 2001, which in turn corresponds to French Application No 00/14488 filed on Nov. 10, 2000 and priority is hereby claimed under 35 USC § 119 based on these applications. Each of these applications are hereby incorporated by reference in their entirety into the present application.
BACKGROUND OF THE INVENTIONThrough the use of cryptography, a message can only be read by its recipient. A key is used to encrypt the message. The owner of the key is the only person who can read the message received.
The encryption key must therefore be transmitted by the sender to the recipient of the encrypted message. Transmission is carried out such that only the recipient of the encrypted message receives this encryption key. Interception by a third party of the encryption key is detected by the sender or the recipient. Consequently, the encryption key or the elements of the key detected as having been intercepted are not used to encrypt the message.
The principle of transmitting encryption keys is used, for example, in quantum cryptography. It consists of using physical properties to guarantee the integrity of a received encryption key.
The encryption key consists of a bit sequence. Generally, a photon polarization state is associated with each bit. The light flow, encoded by polarization, is then attenuated. The probability of detecting two photons associated with the same bit is then negligible.
The sender can encode the encryption key on two nonorthogonal states (a given polarization state and a state at 45°). Concerning this subject, Bennett wrote the article “Quantum Cryptography using any two Nonorthogonal states” in Physics Review letters 68 in 1992. In reception, the detection states are chosen in a base with two states. These two detection states are orthogonal respectively to each state of the base used by the sender. During transmission, the transmission and detection states are chosen independently of each other.
If the states chosen by the transmitter and the receiver are orthogonal, the detection probability is zero. The measurement result is certain, there is no ambiguity. If they are not orthogonal, there are two possible measurement results since the probability of detecting the photon is 0.5. If the photon is detected, it is certain that the transmitter state is at 45° to the receiver state. There is no ambiguity. Irrespective of the polarization configuration, there is always a possibility of not detecting the photon. This non detection of the photon makes deducing the choice of transmitter polarization, using the receiver state, ambiguous.
This ambiguity concerning the polarization is used in quantum cryptography. A non recipient cannot reproduce the message since it is impossible to avoid losing information.
This type of quantum cryptography is known as “polarization ambiguity quantum cryptography” since it uses photon polarization states. A certain number of problems are to be faced. They concern the encoding of the encryption key on the polarization states of the photons in a light flow. During transmission, there is a problem of polarization distortion. For example, transmission by optical fibers requires complex systems which are difficult to implement and very expensive. For example,
-
- either the use of polarization-maintained fibers, which are expensive and difficult to implement,
- or the use of complex systems implementing, for example, Faraday rotators.
This invention proposes an alternative: quantum cryptography by ambiguity in time. It is easier to implement since protected, amongst other things, against problems of transmission by optical fibers. Two photons transmitted successively with a time difference Δt will be received in the transmission order with the same time difference Δt, independently of the transmission medium.
The invention concerns a digital data encoding method intended for transmission by particle flow such that the probability of transmitting two particles per period is negligible, wherein it includes the transformation of the sequence of K bits of digital data in a train of K pulses of particle flows of time width ΔT whose frequency Tb is predetermined, knows that each of the K pulses being shifted or not in time such that the kth pulse is shifted by a duration t0, respectively t1, with respect to the initial instant of the period depending on the value “0”, respectively “1” of the kth bit, where k is an integer such that 0≦k<K and the shifts t0 and t1 are such that 0≦t0,t1≦Tb−ΔT and 0<|t1−t0|<ΔT.
Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description thereof are to be regarded as illustrative in nature, and not as restrictive.
The invention proposes a method to decode digital data encoded according to the procedure wherein, given Δt=ΔT−lt1−t0l, it comprises:
-
- observation of the flow of particles received on one or two time windows for each bit reception period of duration Tb,
- detection of particles in the time observation window(s) generates either a bit of value “0” or “1”, or a signal indicating ambiguity.
The advantages and features of the invention will be clearer on reading the following description, given as an example, illustrated by the attached figures representing in:
The principle of this invention is based on the reproduction of the state of the art polarization ambiguity arrangement in the time domain.
The information is encoded in pulses of time width ΔT as shown on
More explicitly, the decoding comprises:
-
- observation of the flow of particles received on one or two time windows for each bit reception period of duration Tb,
- if t0<t1, the first time observation window starts at instant t0 (inclusive) and ends at instant t1 (exclusive), the second observation window starts, if necessary, at instant t1+Δt (exclusive) and ends at instant t1+T (inclusive) or vice versa,
- if t1<t0, the first time observation window starts at instant t1 (inclusive) and ends at instant t0 (exclusive), the second observation window starts, if necessary, at instant t0+Δt (exclusive) and ends at instant t0+T (inclusive) or vice versa,
- detection of particles in the time observation window(s) generates:
- a bit of value “0”:
- if t0<t1, when a particle is detected in the window starting at t0 of period k,
- if t1<t0, when a particle is detected in the window starting at t0+Δt of period k,
- a bit of value “1”:
- if t1<t0, when a particle is detected in the window starting at t1 of period k,
- if t0<t1, when a particle is detected in the window starting at t1+Δt of period k,
- a signal indicating an ambiguity on the bit value if no particle was detected in the first, and if necessary, in the second observation window.
- a bit of value “0”:
- observation of the flow of particles received on one or two time windows for each bit reception period of duration Tb,
In our example, the bits are transmitted according to the format of
The particle flow pulses carrying the information to be transmitted in time shifted format are, for example:
-
- [ENCODER A] Either produced directly by an encoded pulse source 11+3 (for example, a laser generating a discontinuous laser beam according to the diagram of encoded pulses shown on
FIG. 1 ), - [ENCODER B] Or shifted in time by t0 or t1 depending on the data to be encoded by a controllable delay gate 13 receiving a particle pulse flow from a pulse source 11+2,
- [ENCODER C] Or chopped with the appropriate time shift (t0 or t1) depending on the data to be encoded by an encoded pulse chopper 12+3 at frequency Tb in a continuous beam from a laser 11,
- [ENCODER D] Or chopped by a pulse chopper 12 at frequency Tb in a continuous beam from a source 11 then given a time shift of t0 or t1 depending on the data to be encoded by a controllable delay gate 13,
- [ENCODER A] Either produced directly by an encoded pulse source 11+3 (for example, a laser generating a discontinuous laser beam according to the diagram of encoded pulses shown on
The various encoders 1 and decoders 3 considered on
[ENCODER A] The first variant of encoder 1 is not illustrated. Encoder 1 includes at least one encoded pulse source 11+3. It produces particle flow pulses of time width ΔT and frequency Tb. In addition, the pulses from this source are shifted by t0 or t1 depending on the value of the data bits to be encoded. The values of the time shifts t0 and t1 are such that 0≦t0,t1≦Tb−ΔT and 0<lt1−t0l<ΔT. In our example, the source 11+3 is a laser, for example a mode-locked laser producing light pulses according to the diagram on
[ENCODER B]
[ENCODER C] The first example of realization of the third variant of encoder 1 shown on
This first example of realization of the third variant of encoder 1 therefore includes a source 11 producing a continuous flow of particles followed by an encoded pulse chopper 12+3 with at least one modulator 121 receiving the continuous flow, and a polarizer 122 to allow transmission only during the recorded pulse.
Another technique consists of using a mechanical chopper 123 which chops pulses of given time width ΔT at the desired frequency Tb on a continuous particle flow.
A disc 1232 with two openings like that shown on
The two pulses are created on two separate beams since they have orthogonal polarizations, as shown on
The third example of realization of the third variant of encoder 1 shown on
The selection device described by the fourth example of realization of the third variant of encoder 1 on
The examples of realization of the third variant of encoder 1 on
[ENCODER D] The fourth variant of encoder 1 is not illustrated. It includes a source supplying a continuous particle flow (single mode laser, etc.) Pulses of time width ΔT are chopped at frequency Tb in the continuous flow. They are produced by a pulse chopper 12 generating pulses either not shifted, or all shifted by t (0≦t≦Tb−ΔT). The structure of the pulse chopper 12 may, for example, be similar to that of the encoded pulse choppers 12+3 described above. The pulses are then shifted or not by a delay gate 13 (for example similar to that of the second variant of encoder 1). The pulses output from the delay gate 13 then carry the data to be transmitted according, for example, to the diagram on
Once the data is encoded as pulses shifted or not by an encoder 1 including, for example, an encoded pulse chopper 12+3 on the particle flow from a continuous source 11, it must be attenuated. The probability that the decoder 3 represented on
A first variant of the decoder 3 shown on
If the time width ΔT and the spectral width Δv of the pulses transmitted satisfy the minimum state relation Δv.ΔT=1, a second variant of the decoder 3 proposed by
Depending on the type of source (11, 11+2 etc.) used, for example a mode-locked laser, the pulse durations may then lie between 10 ps and 100 fs. These values of much less than the response times of some existing photon counters (typically 1 ns). In this case, the photon counter (31, 31′) cannot distinguish between a shifted pulse and a non-shifted pulse, or between a pulse shifted by t0 and a pulse shifted by t1. This function can then be carried out by using, for example, an optical gate (not shown on the figures) upstream from the photon counter (31, 31′). This gate is electrically controlled It must be fast enough to produce detection gates of sufficiently short duration corresponding to the observation windows of
The decoder 3 shown on
An additional advantage of time ambiguity cryptography over polarization ambiguity cryptography is that the probability of the decoder 3 detecting a photon is greater when the decoder 3 uses two observation windows.
It will be readily seen by one of ordinary skill in the art that the present invention fulfills all of the objects set forth above. After reading the foregoing specification, one of ordinary skill will be able to affect various changes, substitutions of equivalents and various other aspects of the invention as broadly disclosed herein. It is therefore intended that the protection granted hereon be limited only by the definition contained in the appended claims and equivalents thereof.
Claims
1. A digital data encoding method intended for transmission by particle flow, comprising the steps of:—
- transforming the sequence of K bits of digital data to a train of K pulses of particle of time width ΔT and whose frequency Tb, is predetermined knowing that each of the K pulses being shifted or not in time such that the kth pulse is shifted by a duration t0 respectively t1, with respect to the initial instant of the period depending on the value “0”, respectively “1” of the kth bit, where k is an integer such that 0≦k<K and the shifts t0 and t1 are such that 0≦t0,t1≦Tb−ΔT and 0<ltl−t0l<ΔT whereby the pulse time width shifted by t0 overlaps with the pulse time width shifted by t1 for an overlap time interval Δt=ΔT−lt1−t0l.
2. The encoding method according to claim 1, wherein:
- the particle flow generated is a light flow, a photon flow, an electron flow or a positron flow;
- the shifts t0 and t1 satisfy one or more of the following relations: t1=t0+ΔT/2 or t0=t1+ΔT/2, t0=0 or t1=0;
- the pulses have a spectral width Δv, and the time width ΔT and spectral width Δv of the pulses satisfy the following relation: Δv.ΔT=1;
- the digital data has at least one encryption key.
3. A digital data encoder for use by a signal transmitter on particle flow comprising:
- a device, called continuous source, generating a continuous particle flow;
- a pulse chopper, chopping a train of pulses of time width ΔT and frequency Tb in the continuous particle flow to convert a sequence of K bits of digital data into a train of K pulses of particle of time width ΔT and whose frequency Tb, is predetermined; and
- a delay gate, shifting the pulses chopped in the particle flow to match the values of the bits to be encoded knowing that each of the K pulses being shifted or not in time such that the kth pulse is shifted by a duration t0 respectively t1, with respect to the initial instant of the period depending on the value “0”, respectively “1” of the kth bit, where k is an integer such that 0≦k<K and the shifts t0 and t1 are such that 0≦t0,t1≦Tb−ΔT and 0<It1−t0l<ΔT whereby the pulse time width shifted by t0 overlaps with the pulse time width shifted by t1 for an overlap time interval Δt=ΔT−lt1−t0l.
4. A digital data encoder for use by a signal transmitter on particle flow comprising:
- a pulse source, generating a particle flow as a train of pulses of time width ΔT and frequency Tb, and
- a delay gate which converts the sequence of K bits of digital data into a train of K pulses of particle of time width ΔT and whose frequency Tb, is predetermined, and shifts the pulses in the particle flow to match the values of the bits to be encoded knowing that each of the K pulses being shifted or not in time such that the kth pulse is shifted by a duration t0 respectively t1, with respect to the initial instant of the period depending on the value “0”, respectively “1” of the kth bit, where k is an integer such that 0≦k<K and the shifts t0 and t1 are such that 0≦t0,t1≦Tb−ΔT and 0<lt1−t0l<ΔT whereby the pulse time width shifted by to overlaps with the pulse time width shifted by t1 for an overlap time interval Δt=ΔT−lt1−t0l.
5. A digital data encoder for use by a signal transmitter on particle flow, comprising:
- a continuous source, generating a continuous particle flow;
- an encoded pulse chopper, chopping in the continuous particle flow a train of pulses to convert the sequence of K bits of digital data into a train of K pulses of particle of time width ΔT and frequency Tb with the appropriate time shift depending on the values of the bits to be encoded knowing that each of the K pulses being shifted or not in time such that the kth pulse is shifted by a duration t0 respectively t1, with respect to the initial instant of the period depending on the value “0”, respectively “1” of the kth bit, where k is an integer such that 0≦k<K and the shifts t0 and t1 are such that 0≦t0,t1≦Tb−ΔT and 0<lt1−t0l<ΔT whereby the pulse time width shifted by t0 overlaps with the pulse time width shifted by t1 for an overlap time interval Δt=ΔT−lt1−t0l.
6. The encoder according to claim 3, wherein it has one or more of the following characteristics:
- a source (11 or 11+2 or 11+3) generates a photon flow,
- the time shifts t, t0 and t1 satisfy one or more of the following relations: t1=t0+ΔT/2 or t0=t1+ΔT/2, t0=0 or t1=0,
- the time width ΔT and the spectral width Δv of the pulses satisfy the following relation: Δv.ΔT=1;
- the digital data has at least one encryption key.
7. A digital data transmitter including at least one digital data encoder for use on a particle flow, the encoder being configured to:
- convert the sequence of K bits of digital data into a train of K pulses of particle of time width ΔT and whose frequency Tb, is predetermined knowing that each of the K pulses being shifted or not in time such that the kth pulse is shifted by a duration t0 respectively t1, with respect to the initial instant of the period depending on the value “0”, respectively “1” of the kth bit, where k is an integer such that 0≦k<K and the shifts t0 and t1 are such that 0≦t0,t1≦Tb−ΔT and 0<lt1−t0l<ΔT whereby the pulse time width shifted by t0 overlaps with the pulse time width shifted by t1 for an overlap time interval Δt=ΔT−lt1−t0l, wherein the encoder is downstream from an attenuator.
8. A method to decode digital data encoded according to a method of claim 1, wherein,
- the digital data is a train of K pulses converted from a sequence of K bits of digital data, of time width ΔT whose frequency Tb, is predetermined knowing that each of the K pulses being shifted or not in time such that the kth pulse is shifted by a duration t0 respectively t1, with respect to the initial instant of the period depending on the value “0”, respectively “1” of the kth bit, where k is an integer such that 0≦k<K and the shifts t0 and t1 are such that 0≦t0,t1≦Tb−ΔT and 0<lt1−t0l<ΔT whereby the pulse time width shifted by t0 overlaps with the pulse time width shifted by t1 for an overlap time interval Δt=ΔT−lt1−t0l, the method comprising the steps of:
- observing the flow of particles received on one or two time windows for each bit reception period of duration Tb, if t0<t1, the first time observation window starts at instant t0 (inclusive) and ends at instant t1 (exclusive), the second observation window starts at instant t1+Δt (exclusive) and ends at instant t1+T (inclusive), if t1<t0, the first time observation window starts at instant t1 (inclusive) and ends at instant t0 (exclusive), the second observation window starts at instant t0+Δt (exclusive) and ends at instant t0+T (inclusive),
- detecting particles in the time observation window(s) and generating: a bit of value “0”: if t0<t1, when a particle is detected in the window starting at t0 of period k, if t1<t0, when a particle is detected in the window starting at t0+Δt of period k, a bit of value “1”: if t1<t0, when a particle is detected in the window starting at t1 of period k, if t0<t1, when a particle is detected in the window starting at t1+Δt of period k, a signal indicating an ambiguity on the bit value if no particle was detected in the first and in the second observation window.
9. The decoding method according to claim 8, wherein, when the time width ΔT and the spectral width Δv of the pulses used by the encoding method satisfy the following relation: Δv.ΔT=1, it comprises one or more of the following steps:
- a filtering step which only allows the particles of spectral width Δv to pass, carried out upstream from observation and detection;
- a count of the number NΔV of particles received of spectral width equal to Δv, a count of the number NΔf of particles received of different spectral width Δf (Δf≠Δv) and a comparison of these two numbers NΔv and NΔf such that if NΔv<NΔf, the interception of particles by a third party is indicated.
10. A decoder of digital data encoded by an encoder of claim 3, wherein the digital data is a train of K pulses converted from a sequence of K bits of digital data, of time width ΔT whose frequency Tb, is predetermined knowing that each of the K pulses being shifted or not in time such that the kth pulse is shifted by a duration to respectively t1, with respect to the initial instant of the period depending on the value “0”, respectively “1” of the kth bit, where k is an integer such that 0≦k<K and the shifts t0 and t1 are such that 0≦t0,t1<Tb−ΔT and 0<lt1−t0l<ΔT whereby the pulse time width shifted by to overlaps with the pulse time width shifted by t1 for an overlap time interval Δt=ΔT−lt1−t0l, and the decoder is configured to:
- observe the flow of particles received on one of the two time windows of the bit reception period of duration Tb, if t0<t1, the first time observation window starts at instant to (inclusive) and ends at instant t1 (exclusive), the second observation window starts at instant t1+Δt (exclusive) and ends at instant t1+T (inclusive), if t1<t0, the first time observation window starts at instant t1 (inclusive) and ends at instant to (exclusive), the second observation window starts necessary, at instant to +Δt (exclusive) and ends at instant t0+T (inclusive),
- wherein the decoder includes a particle counter for detecting the presence or not of particles in the time observation window(s) and for generating: a bit of value “0”: if t0<t1, when a particle is detected in the window starting at t0 of period k, if t1<t0, when a particle is detected in the window starting at t0+Δt of period k, a bit of value “1”: if t1<t0, when a particle is detected in the window starting at t1 of period k, if t0<t1, when a particle is detected in the window starting at t1+Δt of period k, a signal indicating an ambiguity on the bit value if no particle was detected in the first and in the second observation window.
11. The decoder according to claim 10, wherein the decoder comprises at least a first particle counter which only counts the particles present in the observation window(s) wherein, when the time width ΔT and the spectral width Δv of the pulses used by the encoder (1) satisfy the following relation: Δv.ΔT=1, it also comprises one or more of the following devices:
- a filter which only allows the particles of spectral width Δv to pass to the first particle counter;
- the first particle counter (31′) generating the number NΔv of particles it detects, a second counter (31″) generating the number NΔf of particles received by the decoder (3) and of spectral width Δf different from Δf≠Δv, a comparator (32) of these two numbers NΔv and NΔf such that if NΔv<NΔf, it generates a predetermined signal indicating either ambiguity of the bit value or interception of particles by a third party.
12. The transmitter of claim 9, further comprising a quantum cryptography to transmit an encryption key to a receiver synchronized with the transmitter due to the secondary beam transmitted by the transmitter.
13. A digital data encoding method according to claim 1, wherein the shifts t0 and t1 satisfy one or more of the following relations:
- t1=t0+ΔT/2 or t0=t1+ΔT/2,
- t0=0 or t1=0.
14. A digital data encoding method according to claim 1, wherein the time width ΔT and the spectral width Δv of the pulses satisfy the following relation: Δv.ΔT=1.
15. A digital data encoding method according to claim 1, wherein the digital data has at least one encryption key.
16. The encoder according to claim 3, further comprising a pulse chopper, chopping a train of pulses of time width ΔT and frequency Tb in the continuous particle flow.
17. The encoder according to claim 16, further comprising a delay gate, shifting pulses chopped in the particle flow to match the values of the bits to be encoded.
18. The encoder according to claim 3, wherein it has one or more of the following characteristics:
- the source (11 or 11+2 or 11+3) generates a photon flow.
- the time shifts t, t0 and t1 satisfy one or more of the following relations: t1=t0+ΔT/2 or t0=t1+ΔT/2, t0=0 or t1=1,
- the time width ΔT and the spectral width Δv of the pulses satisfy the following relation: Δv.ΔT=1;
- the digital data has at least one encryption key.
19. A decoder of digital data encoded by an encoder of claim 4, wherein the digital data is a train of K pulses converted from a sequence of K bits of digital data, of time width ΔT whose frequency Tb, is predetermined knowing that each of the K pulses being shifted or not in time such that the kth pulse is shifted by a duration to respectively t1, with respect to the initial instant of the period depending on the value “0”, respectively “1” of the kth bit, where k is an integer such that 0≦k<K and the shifts t0 and t1 are such that 0≦t0,t1<Tb−ΔT and 0<lt1−t0l<ΔT whereby the pulse time width shifted by to overlaps with the pulse time width shifted by t1 for an overlap time interval Δt=ΔT−lt1−t0l, and the decoder is configured to:
- observe the flow of particles received on one of the two time windows of the bit reception period of duration Tb, if t0<t1, the first time observation window starts at instant to (inclusive) and ends at instant t1 (exclusive), the second observation window starts at instant t1+Δt (exclusive) and ends at instant t1+T (inclusive), if t1<t0, the first time observation window starts at instant t1 (inclusive) and ends at instant to (exclusive), the second observation window starts at instant t0+Δt (exclusive) and ends at instant t0+T (inclusive),
- wherein the decoder includes a particle counter for detecting the presence or not of particles in the time observation window(s) and for generating: a bit of value “0”: if t0<t1, when a particle is detected in the window starting at t0 of period k, if t1<t0, when a particle is detected in the window starting at to +Δt of period k, a bit of value “1”: if t1<t0, when a particle is detected in the window starting at t1 of period k, if t0<t1, when a particle is detected in the window starting at t1+Δt of period k, a signal indicating an ambiguity on the bit value if no particle was detected in the first and in the second observation window.
20. A decoder of digital data encoded by an encoder of claim 5, wherein the digital data is a train of K pulses converted from a sequence of K bits of digital data, of time width ΔT whose frequency Tb, is predetermined knowing that each of the K pulses being shifted or not in time such that the kth pulse is shifted by a duration to respectively t1, with respect to the initial instant of the period depending on the value “0”, respectively “1” of the kth bit, where k is an integer such that 0≦k<K and the shifts t0 and t1 are such that 0≦t0,t1<Tb−ΔT and 0≦lt1−t0l<ΔT whereby the pulse time width shifted by to overlaps with the pulse time width shifted by t1 for an overlap time interval Δt=ΔT−lt1−t0l, and the decoder is configured to:
- observe the flow of particles received on one of the two time windows of the bit reception period of duration Tb, if t0<t1, the first time observation window starts at instant t0 (inclusive) and ends at instant t1 (exclusive), the second observation window starts at instant t1+Δt (exclusive) and ends at instant t1+T (inclusive), if t1<t0, the first time observation window starts at instant t1 (inclusive) and ends at instant to (exclusive), the second observation window starts at instant to +Δt (exclusive) and ends at instant t0+T (inclusive),
- wherein the decoder includes a particle counter for detecting the presence or not of particles in the time observation window(s) and for generating:
- a bit of value “0”: if t0<t1, when a particle is detected in the window starting at t0 of period k, if t1<t0, when a particle is detected in the window starting at t0+Δt of period k,
- a bit of value “1”: if t1<t0, when a particle is detected in the window starting at t1 of period k, if t0<t1, when a particle is detected in the window starting at t1+Δt of period k,
- a signal indicating an ambiguity on the bit value if no particle was detected in the first and in the second observation window.
21. The encoder according to claim 4, wherein:
- a source (11 or 11+2 or 11+3) generates a photon flow,
- the time shifts t, t0 and t1 satisfy one or more of the following relations: t1=t0+ΔT/2 or t0=t1+ΔT/2, t0=0 or t1=0,
- the time width ΔT and the spectral width Δv of the pulses satisfy the following relation: Δv.ΔT=1;
- the digital data has at least one encryption key.
22. The encoder according to claim 5, wherein:
- a source (11 or 11+2 or 11+3) generates a photon flow,
- the time shifts t, t0 and t1 satisfy one or more of the following relations: t1=t0+ΔT/2 or t0=t1+ΔT/2, t0=0 or t1=0,
- the time width ΔT and the spectral width Δv of the pulses satisfy the following relation: Δv.ΔT=1;
- the digital data has at least one encryption key.
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Type: Grant
Filed: Nov 9, 2001
Date of Patent: Nov 20, 2007
Patent Publication Number: 20040062396
Assignee: Thales (Neuilly-sur-Seine)
Inventor: Thierry Debuisschert (Orsay)
Primary Examiner: Gilberto Barron
Assistant Examiner: Devin Almeida
Attorney: Lowe Hauptman Ham & Berner, LLP
Application Number: 10/416,187
International Classification: H04K 1/00 (20060101);